Poté co zálivka skončí, necháme substrát prosychat.

Poté co means after in the sense of after/once a certain thing happens.

So:

• Poté co zálivka skončí = after the watering ends

Literally, poté is something like after that / then, but together with co it functions as a conjunction introducing a subordinate clause.

You may also see very similar expressions such as:

• potom co = after
• jakmile = as soon as
• až = when/once

In this sentence, poté co is a fairly neutral written way to say after.

Because Czech uses a comma to separate a subordinate clause from the main clause.

Here the subordinate clause is:

• Poté co zálivka skončí

And the main clause is:

• necháme substrát prosychat

So the comma marks the boundary between them:

• Poté co zálivka skončí, necháme substrát prosychat.

This is very similar to English:

• After the watering ends, we let the substrate dry out.

If the order were reversed, the comma would still separate the two clauses:

• Necháme substrát prosychat, poté co zálivka skončí.

Both relate to watering, but they are not exactly the same.

• zálivka = a watering, irrigation, the watering event or application of water
• zalévání = watering as an activity or process

In gardening or plant-care instructions, zálivka is very common because it refers to a concrete watering cycle or dose of water. It sounds a bit more technical or horticultural.

So:

• Poté co zálivka skončí = after the watering is finished
• Poté co zalévání skončí would also be understandable, but it sounds more like the activity/process of watering.

Because skončit is a perfective verb.

In Czech, perfective verbs do not normally have a true present meaning. Their present-looking forms usually refer to the future.

So:

• skončí literally looks like present tense
• but it means will end / ends (in the future)

That is why:

• Poté co zálivka skončí = after the watering ends / has ended

Compare:

• končí from končit (imperfective) = is ending / ends habitually
• skončí from skončit (perfective) = will end, reaches completion

English speakers often need time to get used to this, because Czech uses aspect here where English relies more on tense.

All of those ideas are close, and context matters.

Necháme is from nechat, which can mean:

• to let
• to leave
• to allow

In this sentence, it means something like:

• we let the substrate dry out
• we leave the substrate to dry out

Because nechat is perfective, necháme can also have a future sense: we will let / we then let.

In instructions, Czech often uses 1st person plural like this in a neutral, practical style:

• uděláme
• přidáme
• necháme

This is similar to English instructional style like:

• then we add...
• then we let it dry...

It does not necessarily mean a literal group of we; it is often just a polite, impersonal way of giving instructions.

Because Czech usually omits subject pronouns when they are not needed.

The ending of the verb already tells you the subject:

• necháme = we let / we will let

So my (we) is unnecessary unless you want emphasis or contrast.

Czech does this all the time:

• Jdu. = I’m going.
• Máme čas. = We have time.
• Uděláte to? = Will you do it?

So in this sentence, the we is built into necháme.

This is a very common Czech pattern:

• nechat + object + infinitive

It means:

• to let something/someone do something
• to leave something/someone doing something

So here:

• necháme = we let / leave
• substrát = the substrate
• prosychat = dry out gradually

Together:

• necháme substrát prosychat = we let the substrate dry out

A few similar examples:

• Nechám děti spát. = I’ll let the children sleep.
• Nechali motor běžet. = They left the engine running.
• Nechte těsto kynout. = Let the dough rise.

The noun after nechat is grammatically the object of nechat, but semantically it is the thing performing the infinitive action.

Substrát is the direct object of necháme, so it is in the accusative case.

However, substrát is a masculine inanimate noun, and for many masculine inanimate nouns, the accusative singular looks the same as the nominative singular.

So:

• nominative: substrát
• accusative: substrát

That is why the form does not change.

Compare:

• Vidím stůl. = I see a table.
  (stůl also stays the same in the accusative)
• Vidím muže. = I see a man.
  Here the accusative changes because muž is masculine animate.

Prosychat means something like:

• to dry out gradually
• to become somewhat dry
• to dry through, little by little

In gardening language, it often refers to soil or substrate losing moisture between waterings, rather than becoming totally bone dry.

So this sentence suggests:

• don’t keep the substrate constantly wet
• allow it to dry somewhat after watering

That nuance is important. It is not just a general dry; it suggests a gradual or partial drying process.

Because prosychat is imperfective, while proschnout is perfective.

That difference affects the nuance:

• prosychat = to be drying out gradually / to dry out over time
• proschnout = to dry through completely, as a completed result

After nechat, the imperfective often sounds more natural when you mean allow the process to happen:

• necháme substrát prosychat = we let the substrate dry out gradually

If you said:

• necháme substrát proschnout

that would focus more on the completed result: we let the substrate dry through completely. Depending on context, that may sound stronger than intended.

So prosychat is a good choice if the point is controlled, gradual drying between waterings.

Yes. Czech word order is flexible, and the original order is natural because it puts the time condition first.

Original:

• Poté co zálivka skončí, necháme substrát prosychat.

A different order could be:

• Necháme substrát prosychat poté co zálivka skončí.

Both are understandable. The original sounds especially natural in instructions because it first sets up the condition/time frame:

• After the watering ends...
• then we let the substrate dry out.

So the chosen word order helps the sentence flow clearly and logically.